AACGM system assumes that magnetic data are best organized along the magnetic field lines. AACGM gives the same magnetic coordinates to any position which lies on the same geomagnetic field line.

It is therefore conceptually closely related to Invariant magnetic coordinates. Thus, a point in space is defined by the geomagnetic field line it is on (given by the latitude and longitude), and its altitude.

To determine the AACGM coordinates of any point, start at that point and use the IGRF magnetic field model to trace the field line to the geomagnetic equator. Then, use the pure magnetic dipole model to trace the magnetic field line back to the surface of the earth. At that point, measure the angle between the line joining the point on the earth with the center of the earth, and the axis which defines the magnetic dipole. This angle gives you the co-latitude of the point in the magnetic coordinates. Any two points connected by a magnetic field line will have the same magnetic latitude and longitude in the AACGM coordinate system